The present invention relates to a breathable backing or release liner and to a process for preparing the same wherein a radiation-cured silicone release coating is provided on essentially only one surface of a woven or non-woven support and high adhesion is obtained on the opposite surface.
Breathable backings are used in a number of applications including in making breathable surgical tape and in diaper tapes for disposable diapers.
Breathable surgical tapes are the subject of several prior patents including U.S. Pat. Nos. 3,121,021 to Copeland (1964), 3,364,063 to Satas (1964), 3,523,846 to Muller (1970), 3,677,788 to Zirnite (1972), 4,202,925 to Dabroski (1980), and 4,427,737 to Cilento et al.
The patents to Zirnite and Dabroski disclose a self-wound surgical tape which is constructed with an active adhesive coating on one surface of a non-woven fabric backing or support and with a release layer on the opposite surface. According to the Zirnite disclosure, the preferred release coating is a stearyl methacrylate acrylonitrile copolymer. Silicone-release backsizes are also disclosed but considered less satisfactory. Dabroski discloses that silicone backsizes may be used, but discloses a preference for water-based backsizes for their non-penetrable viscosity. In accordance with Dabroski's preferred embodiment, two release backsizes are sequentially applied to the support. The first is a styrene ethylacrylate-butadiene copolymer. The second is a silicone-release agent which is applied after drying the first.
According to both the Zirnite and Dabroski patents, the release coatings are applied using conventional application techniques. Gravure roll coating and spray coating techniques are disclosed. The gravure roll coating technique is disclosed as the preferred means.
The silicone release coatings used in the aforementioned breathable tape backings are formed using thermally-cured solvent-based or aqueous-based coating compositions. These backings frequently do not exhibit adequate adhesion for the adhesive composition, particularly when the release coating is applied to the backing before the adhesive composition. Breathable backings, are highly permeable and readily penetrated by solvent-based or aqueous-based release coating compositions. Consequently, a portion of the release coating strikes through the backing to the uncoated opposite surface and reduces the adhesion at that surface for the adhesive composition. There is also a tendency for thermally-cured compositions to offset to the opposite surface of the backing.
While adhesion may be improved if the release coating is applied after the adhesive, the preferred method for making breathable adhesive tapes is to apply the release coating first. It is not desirable to apply the adhesive first because the adhesive-coated backing is difficult to handle and, therefore, is difficult to coat with the release coating. By contrast, the release-coated backing is easily handled and readily coated with the adhesive. In addition, in the manufacture of surgical tapes, it is particularly important to keep the adhesive clean during processing so that a sterile and aseptic product is obtained. This is very difficult to do if the release coating is applied after the adhesive.